Let's go even further. The theatre is created from the very beginning, and even the naval invasion would be fully simulated in the background as part of the army being assigned to the theatre. Hands-off means you don't have to manually set up any invasions.
Depending on the task (=wargoals), you'd have a rough estimate of how much resources your general needs. You give him that, and he goes off and tries to accomplish it. After a while you get first results, and can accept the outcome, or continue to keep it going.
Wars would initially only be fought over the war goals and leave everything else untouched, with limited expeditionary forces assigned to the limited tasks. If one side escalates (by widening the scope of the war, by sending more troops, involving other powers etc.), it eats a hefty infamy penalty, opens itself to more wargoals, possible mid-war intervention from other powers, and more theatres become available.
I'd also discourage total wars. Not just with an infamy penalty for repeated escalations, but by raising the stakes. If one side escalates and the mainland becomes the target of the war, and one side fights until its entire homeland (capital included) is occupied? Then you're at the total mercy of the victors, who can (and will!) disband your armies, scuttle your fleets, distribute all your colonies, depose your government, change your laws, and shatter your nation.
Yes, looking at you, Queen Victoria, off to Elba with you. You cause hundreds of thousands of deaths over reducing the autonomy of Lanfang and didn't know when to stop? You better believe that this is the end of you. Remember, the Treaty of Versailles, the Treaty of Trianon, the Treaty of Saint Germain, they were all in the timeframe of the game. Cause a world war? Suffer the consequences of losing one. Would take a while for most nations to gear up for war again, and we'd have peace for our time.